Biology Exam 4 (part of Final Exam)

The branch of biology that deals with fertilization, early growth, and development of living organisms.

*Animals in major groups with the same general body plan.

* Embryos of "higher" forms go through stages that resemble "lower" forms.

*Embryos of species in same group resemble one another. Ex. Goose neck barnacles and brine shrimp.

* Recapitulation: A brief summary.

*Reflects phylogeny? A ladder of evolution.

*"Ontogeny (developmental growth) recapitulates (short summary) phylogeny (evolutionary history).

*Development of an individual repeats the evolutionary history of a species."

*Evolution proceeds by adding modifications onto pre-existing states.

Studied chick embryos, mammalian development from eggs.

*General characters appear earlier in development than special characters.

*Embryos of "higher" species are like the embryos of "lower" species but not like adults.

*The embryo of a species does not pass through definite forms but progressively differs from them.

Mammals, Birds, Reptiles, Amphibians, Bony fishes, Sharks and rays, Jawless vertebrates, Lancets, Tunicates.

*Dorsal, hollow nerve cord.
*Notochord--stiff rod.
*Pharyngeal gill slits.
*Tail.

1 cell.

Hollow single layer, ball of cells. Means "little sprout."

3 tissue layers. Means "little stomach."

Tubular structures. Means "little nerve."

Differentiated along axis.

*Egg divided into animal hemisphere and vegetal hemisphere. Cortical cytoplasm and inner cytoplasm.

*Egg has radial symmetry: Both halves the same.

*Sperm will contact the egg and enter into the animal hemisphere.

Cortical cytoplasm has shifted and overlies the inner cytoplasm. This establishes polarity and gives the egg bilaterial symmetry.